Ion beam deflection system



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ION BEAM DEFLECTION SYSTEM Filed June 14. 1966 2 Sheets-Sheet 2 404 64 606 7 M4.) a P K I 12a 5.

Irma n4 United States Patent 3,535 880 ION BEAM DEFLECTION SYSTEM George A. Work and George R. Brewer, Malibu, Califi, assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed June 14, 1966, Ser. No. 557,424 Int. Cl. F02k 1 1 0.0

U.S. Cl. 60-202 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an ion engine of the type wherein thrust is obtained by emitting an ion beam passing through a deflection electrode. This electrode comprises first and second conductive members positioned on opposite sides of the ion beam and extending in the direction of the ion beam a predetermined distance. The direction of the thrust of the ion engine is altered by applying push-pull deflection potentials to the first and second members in order to deflect the ion beam to a desired angle. Third and fourth conductive members may also be added and arranged with the first and second members as sectors of a circle around the ion beam so as to provide deflection of the ion beam along an axis extending between respective opposite members when separate push-pull potentials are applied.

One of the types of electric propulsion engines which is being considered for application to satellite control is known as an ion engine. There are low thrust applications where the simplicity, eflicient propellant utilization, long life, and reliability of these devices warrant their use.

In order to control the attitude and/or position of a space vehicle, where it is proposed to use an ion engine, it has been proposed to mount the ion engine on gimbals and to mechanically pivot the engine to direct the thrust of the ion engine in different directions. Alternatively, it has been proposed to use a plurality of ion engines which are mounted at diiferent locations about the space vehicle whereby turning on and off diflerent ones of these engines controls the direction of thrust and thereby the attitude or position of the space vehicle. Neither of these arrangements is satisfactory since they add to the weight of the space vehicle, and more important add to the complexity of the control system required.

An object of this invention is the provision of an improved ion engine whose direction of thrust may be controlled more simply than heretofore.

Yet another object of the present invention is the provision of a novel ion beam deflection control system.

Still another object of the present invention is the provision of a simple arrangement for controlling the direction of thrust of the ion beam which is emitted from an ion engine.

The above and other objects of this invention are achieved by using a deflection electrode for the ion beam. This may be done by forming the accelerator electrode of the engine into opposite spaced segments which are insulated from one another and between which the ion beam being emitted by the engine passes. By the application of push-pull voltages to opposite ones of these segments, the angle at which the ion beam is emitted from the ion engine may be varied to change the direction of the thrust which is applied to the vehicle carrying the ion engine. In one embodiment where the ion beam is circular in cross section, four deflection members are placed in quadrants, and the ion beam can be deflected in two axes. In another embodiment of the invention, wherein the ion beam is emitted from a long, rectangular ionizer, the accelerator electrode may be formed into two spaced apart portions which are coextensive with the ion beam and between which it passes. Here too, the application of a push-pull voltage to the opposite portions of the electrode causes the ion beam to be deflected whereby its direction of thrust is controlled in one axis whereby the direction or attitude of the vehicle carrying the ion engine is controlled.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an ion beam engine incorporating a deflecting electrode in accordance with this invention;

FIG. 2 is a schematic isometric view of an embodiment of the invention shown in FIG. 1;

FIG. 3 shows a schematic diagram illustrative of a circuit which can be employed for applying the requisite control voltages to the deflection electrode used in accord ance with this invention;

FIGS. 4 and 5 are plan and elevation views of a defiection electrode in accordance with this invention which is employed for a rectangular type of ion beam; and

FIG. 6 is a schematic drawing of an ion engine having a separate accelerating electrode and a deflection electrode in accordance with this invention.

Referring now to FIG. 1, there may be seen a schematic drawing of a type of ion engine known as a cesiumcontact ion engine, which also includes a deflecting electrode in accordance with this invention. The deflection electrode described in accordance with this invention may be used with other types of ion engines, the type shown and described here being considered merely as exemplary. The ion engine is carried in a space vehicle, which is not shown here, and includes a cesium reservoir 10, which vaporizes cesium atoms. These are directed through an ionizer 12, which is customarily made of heated porous tungsten and has the effect of depriving the cesium atom of an electron in its passage therethrough, whereby the output consists of cesium ions.

The cesium ions next pass through the spaced apart portions of an electrode 14, which heretofore has served the purpose so ely of an accelerating electrode to increase the electric field at the ionizer and to increase the emitted ion current in accordance with well known physical principles relating current to the three halves power of the accelerating voltage. It was not shaped in the manner which is to be described for the invention herein but merely had an opening therein and was biased by voltages in order to increase the current drawn from the ionizer. When an ion passes through the accelerator electrode, its velocity is decreased by the application of other potentials, and no net electrical power is normally consumed in the accelerator electrode circuit. This method is standard procedure in the ion engine technology and allows for high efliciency at relatively low main drive or ionizer potentials, which provides the thrust by electrical forces on the cesium ions. The accelerated column of ions would next pass through an exit electrode 16. The potentials required for operating the ion engine were provided by a main drive positive potential source 18 connected between the ionizer and ground. A negative voltage 20 was connected between the accelerating electrode and ground to provide the high electric field required for large ion currents. While the above description is given in terms of the cesium-contact type ion engine, it is to be understood that this is an example only; the deflection technique disclosed can be applied to any other type 3 of ion accelerator, e.g., one in which the ionization is provided by means of electron bombardment.

In order to controllably deflect the ion beam in accordance with this invention, the accelerating electrode is given the form illustrated in FIG. 2. There, it may be seen that the accelerating electrode is divided into four quadrants respectively 14X 14X;, 14Y and 14Y Referring back to FIG. 1, it will be seen that there is a flange 14F attached to each electrode sector which eX- tends substantially at right angles to the plane of the deflection electrode, adjacent the ion beam (represented by the dotted lines 24) in the direction of the ionizer 12. The length of the flange, a, defines the drift space, or the space over which the field established between the opposite sectors of the deflection electrode have an effect upon the ion beam. It should be appreciated that if the electrode 14 is given the same thickness as the length of the flange a, the same deflection effects are achieved. The use of a flange may be preferred, however, since a thinner electrode with a savings in weight is obtained thereby. The space between the opposite sectors of the deflection electrode 14 at the center is indicated by the dimension d. If the angle is considered as the angle over which the ion beam can be deflected, then Tan B AVa/Vd where V is the potential between the cesium reservoir and the accelerating electrode, and AY is the potential difference between opposite segments of the deflection electrode. Thus, the accelerator electrode when modified in accordance with this invention provides the additional function of controlling the direction of thrust of the ion engine.

FIG. 3 represents the circuit diagram illustrative of how the deflection voltages for controlling the angle of emission of the beam from the ion engine, may be applied to the various sectors of the electrode 14. An input voltage source 30, which may be for example a twentyfour volt, kilocycle source, is applied to a transformer 32, which has two center tapped secondaries respectively 328 and 32S;, Rectifiers respectively 34, 36, 38, 40, are connected between the respective ends of the respective secondary windings 328 and 328 and the output terminals dsignated by X and X and Y and Y to correspond to the sectors of the deflection electrode shown in FIG. 2. Another transformer 42 has its secondary winding 428 connected in series with the center tap of the winding 32S The other end of the secondary winding 428 is connected to the junction of two resistors respectively 44, 46, which have their other ends connected to the terminals X and X Capacitors 48 and 50 are connected in series and across the secondary winding 328 A voltage to produce a desired X deflection is applied to the primary winding 42P of the transformer 42. This is rectified by the diodes 34, 36 and applied as a push-pull voltage to the X X terminals. A source of accelerating voltage is connected to the center taps of secondary windings 328 and 32S The :AX voltage produced by the application of the voltage to the primary winding 42P adds to or substracts from the accelerating voltage.

The :AY voltage is derived in the same manner as the :AX voltage. A transformer 52 has its secondary winding 52S connected in series with the center tap of the secondary winding 328 The primary winding 52F has applied thereto a voltage desired to determine the direction of the ion beam along the Y axis which extends between the two Y deflection electrodes. The arrangement of the capacitors and resistors which merely constitute the other elements of the filter is the same as that described in connection with the X and X voltages.

In an embodiment of the invention which was built, where the voltage :AV was varied, :6 volts, 0 reached 1 degree. At volts, 0 reached 5 degrees, and when AV was volts, 0 reached 10 degrees. Of course, the

same result was obtained along the Y axes applying these voltages to the two Y sectors.

FIG. 4 illustrates a view in elevation of a deflection electrode, in accordance with this invention, which may be employed for deflecting a rectangular cross section beam of ions; and FIG. 5 is a plan view of this electrode. The deflection electrode 60 comprises two spaced apart portions respectively 60A, 60B. These are held spaced apart by insulator bars 62, 64, which are attached to the spaced apart deflector portion 60A, 60B by any suitable fastening means.

As seen in FIG. 5, the width of the deflector portions 60A, 60B flare outwardly from one end to the other. The ion rectangular-shaped beam passes from the narrowest portion of the opening to the widest portion, in the direct1on of the arrows shown in FIG. 5. The narrowest portion has a dimension a and the widest portion has a dimension 0. The thickness of the electrode is indicated by the dimension b and represents the distance over which an electric field is established between the two spaced deflection members 60A, 60B act on the ion ribbon beam. The outward flare of the portions of the two members at the opening therebetween enables the electric field to more uniformly operate on the beam once the beam is deflected. The ribbon beam or strip beam extends substantially the entire length of the space between the two members 60A, 60B and the angle that it makes with respect to the plane normal to the plane of the deflection electrodes is easily controlled by the application of push-pull voltages :AV superimposed upon the accelerator voltage applied to the members of the deflection electrode.

FIG. 6 is a schematic diagram illustrating how an embodiment of this invention may be used in an ion engine which also has a separate accelerating electrode. In this arrangement, the deflection electrode 66 is placed between the accelerating electrode 68 and the ground electrode 70 which is connected to ground. A source of cesium ions 72, including a focusing electrode, is connected to the positive terminal of a high potential source 74, whose negative terminal is grounded. The accelerating electrode is connected to the negative terminal of a high potential source 76, whose positive terminal is grounded. Positive and negative or push-pull deflection potentials are provided from a deflection potential source 78 to the segments of the deflection electrode 66.

The deflection electrode 66 may be of the quadrantal sector type 14 shown in FIG. 2, or of the rectangular slot type 60 shown in FIG. 4, in accordance with the crosssectional area of the ion beam sought to be deflected. The arrangement shown in FIG. 6 has the advantage that the deflection potentials are referenced to ground rather than to a high negative potential as is the case when the deflection electrode also functions as the accelerating electrode.

There has accordingly been described and shown herein a novel, and unique construction for an ion engine wherein the ion beam direction of thrust may be controlled by varying the voltage applied to two conductive members between which the beam passes. Said two conductive members may also perform the function of an accelerator electrode, or may serve solely as a deflection electrode.

What is claimed is:

1. In an ion engine of the type wherein thrust is obtained by emitting an ion beam, means for controlling the direction of the thrust obtained comprising a deflection electrode through which said ion beam passes, said deflection electrode comprising a first and second conductive member positioned on opposite sides of said ion beam, said first and second conductive member having a surface portion thereof extending in the direction of said ion beam a predetermined distance, means for applying an ion beam accelerating voltage to both of said conductive members, and means for applying push-pull deflection potentials to said first and second member to deflect said ion beam at a desired angle to alter the direction of the thrust of said ion engine.

2. In an ion beam thrust engine as recited in claim 1 wherein said deflection electrode has in addition to said first and second deflection members, a third and fourth deflection member, said first, second, third and fourth deflection members being arranged as sectors of a circle around said ion beam, means for applying an ion beam accelerating voltage to all of said deflection members, means for applying a first set of push-pull potentials to said first and second members for deflecting said ion beam along an axis extending between said first and second members, and means for applying a second set of push-pull potentials to said third and fourth members to deflect said ion beam along an axis extending between said third and fourth deflecting members.

3. A deflection electrode for an ion beam engine which generates a substantially cylindrical beam comprising first, second, third and fourth conductive members each having the shape of a substantially quadrantal sector o'f a circle, each being spaced from the other, said first, second, third and fourth deflection members defining a circular opening at the inner ends thereof, through which an ion beam may pass, each of said quadrantal sectors having a flange extending at right angles therefrom at the inner ends thereof adjacent the circular opening, means for applying an ion beam accelerating voltage to all of said 6 conductive members whereby said members operate as an accelerating electrode as well as a deflecting electrode, means for applying a first set of deflection voltages to two of said deflection members which are spaced opposite one another, and means for applying a second set of pushpull deflection voltages to the remaining two of said deflection members which are spaced opposite one another.

References Cited UNITED STATES PATENTS Re. 26,177 3/ 1967 Deutsch 202 2,763,125 9/1956 Kadosch et al. 3l363 3,014,154 12/1961 Ehlers et al 60202 3,015,745 1/1962 Klein 3l363 3,050,652 8/1962 Baldwin 60202 X 3,052,088 9/1962 Davis et al. 60-202 3,071,154 1/1963 Cargill et al. 3,137,801 6/1964 Brooks et al 3l363 FOREIGN PATENTS 1,278,129 10/ 1960 France.

CARLTON R. CROYLE, Primary Examiner US. Cl. X.R. 

